1. Field of the Invention
The present invention relates to a wire dot printer head and a wire dot printer.
2. Discussion of the Background
A wire dot printer head is an apparatus which swings an armature coupled with a wire for printing between a printing position and a waiting position, and when the armature is swung to the printing position, a tip end of the wire comes into collision with a print medium, such as a sheet of paper, whereby printing is carried out.
As an example of such wire dot printer head as described above, in the gazette of Japanese Patent Application laid-open No. 2001-219586, there is disclosed an apparatus in which a magnetic flux induced by a coil around the armature to be swung generates a magnetic circuit for attracting the armature from the waiting position to the printing position, thereby executing a printing. As shown in FIG. 6 and FIG. 7, in the wire dot printer head 100 in the conventional art as described above, an armature 102 which supports a wire 101 for printing has a support shaft 103, and the armature 102 is provided in such a manner as rotatable around the support shaft 103. An armature spacer 105 having a cutout 104 for accommodating the support shaft 103 of the armature 102 is provided on a yoke 106 for generating the magnetic circuit. Further, on the armature spacer 105 there is provided a plate 108 for holding down the support shaft 103 so as to control a movement of the support shaft 103, via an elastic spacer 107 which fixes a position of the support shaft 103 of the armature 102 with elasticity. With this structure, it is possible to prevent an abrasion of the plate 108 due to the support shaft 103 of the armature 102, and thus the position of the support shaft 103 can be fixed.
However, with speed-enhancement in printing in recent years, the armature 102 has to swing between the printing position and the waiting position, for example, 2,500 times per second, thereby causing an intensive oscillation during the printing. As a result, the support shaft 103 being a center of rotational movement of the armature 102 may wear out a surface of the yoke 106. As the abrasion of the surface of the yoke 106 proceeds due to the support shaft 103 of the armature 102, the support shaft 103 of the armature 102 becomes movable and deviated from a predetermined position, causing unstable swinging movement of the armature 102. Consequently, this may become a factor which deteriorates a printing quality.
Furthermore, due to an oscillation according to the speedup in printing, the support shaft 103 of the armature 102 moves not only in the swinging direction of the armature 102 but also into a radial direction of the armature spacer 105. Then, it may also cause unstable swinging movement of the armature 102. Moreover, when the abrasion of the surface of the yoke 106 due to the support shaft 103 of the armature 102 proceeds, for example, the armature 102 may come into contact with a flange of the coil, or may erase the cutout 104 of the armature spacer 105 with a micro motion of the support shaft 103. Consequently, the life of the wire dot printer head 100 may be shortened.